<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>

</head>

<body>
    <style>
        .sm {
            width: 24%;
        }
        
        #big {
            width: 100%;
        }
        
        div {
            width: 400px;
        }
    </style>
    <p>hello</p>
    <div>
        <img src="./images/1.jpg" id='bigone' alt="">
        <img src="./images/1.jpg" class='sm' alt="">
        <img src="./images/2.jpg" class='sm'>
        <img src='./images/3.jpg' class='sm'>
        <img src='./images/4.jpg' class='sm'>
    </div>
    <form action="./jquery-3.3.1.min.js" method='get'>
    <button>jquery1</button>
    </form>
    <form action="./jquery-3.3.1.min.js" method='post'>
    <button>jquery2</button>
    </form>
    <script src='./jquery-3.3.1.min.js'></script>
    <script>
       $('.sm').click(function () {
            bigone.src=this.src
        })
    </script>
</body>

</html>